1. Field of the Invention
The present invention relates to a dispersion type liquid crystal display element useful as, for example, a flat panel display device.
2. Description of the Related Art
Liquid crystal display elements of TN type and of STN type using a nematic liquid crystal have already been put to a practical use. Also, a liquid crystal display element using a ferroelectric liquid crystal is being proposed. In forming such an element, an orientation treatment or the like is required. This requirement is a serious problem to be solved for easily manufacturing a large liquid crystal display element.
On the other hand, methods of manufacturing a large liquid crystal display element at a low cost without depending on such an orientation treatment are disclosed in Published Unexamined Japanese Patent Application No. 58-501631 and U.S. Pat. No. 4,435,047. It is taught in these prior arts that liquid crystal molecules are encapsulated in polyvinyl alcohol or the like so as to disperse the liquid crystal molecules in the polymer. A thin film formed of the polymer prepared by the known method described above can be used for forming a liquid crystal display element. Where the encapsulated liquid crystal molecules exhibit a positive dielectric anisotropy within the thin film, the encapsulated liquid crystal molecules are oriented in the direction of the electric field upon application of an electric field. If the refractive index n.sub.o of the liquid crystal becomes equal to the refractive index n.sub.p of the polymer upon application of the electric field, the liquid crystal element is turned transparent. After removal of the electric field, the liquid crystal molecules are brought back to the state of random arrangement. As a result, the refractive index n.sub.o of the liquid crystal is deviated from the refractive index n.sub.p of the polymer. It follows that the light is scattered at the boundary between the liquid crystal phase and the polymer phase so as to make the liquid crystal display element turbidly.
Other types of a dispersion type liquid crystal display element using a thin film formed of a polymer having liquid crystal molecules dispersed therein are also known to the art. For example, Published Unexamined Japanese Patent Application No. 61-502128 discloses an element, in which liquid crystal molecules are dispersed in an epoxy resin. Also, Published Unexamined Japanese Patent Application No. 2-83534 discloses an element, in which liquid crystal molecules are dispersed in urethane acrylate resin.
Further, Published Unexamined Japanese Patent Application No. 63-66542 discloses a dispersion type liquid crystal display element, in which a fluorescent material is contained in at least one of the liquid crystal material which is to be encapsulated and a supporting medium so as to enable the light emitted from the fluorescent material to improve an effective contrast.
The dispersion type liquid crystal display element described above is certainly simpler in construction than the conventional element constructed such that a liquid crystal material is held between a pair of glass substrates and sealed, making it possible to form easily a larger element. In the dispersion type liquid crystal display element, however, a voltage application to the element simply brings about transmission and scattering of light, though the voltage application directly leads to an improved brightness of the background light in the conventional device noted above. To be more specific, when it comes to a dispersion type liquid crystal display element, light is scattered when voltage is not applied to the element so as to make the element white, and the element is made transparent upon voltage application. It should be noted that, in the dispersion type liquid crystal display element, the contrast is determined by the ratio in intensity of the transmitting light to the scattered light. Thus, in order to improve the contrast, it is necessary to collect the parallel transmitting light alone by, for example, diminishing the collecting angle of the scattered light in a dark state. Under the circumstances, Published Unexamined Japanese Patent Application No. 63-98631 discloses a liquid crystal display element, in which the encapsulated liquid crystal material comprises a background light supply portion and a selective light transmitting portion. However, the liquid crystal display element disclosed in this prior art necessitates a shutter serving to form a group of converging lenses and a group of apertures corresponding to the picture element regions, making it difficult to manufacture a large liquid crystal display element with a low cost.